Tenofovir, also known as 9-[2-(R)-(phosphonomethoxy)propyl]adenine (PMPA), is represented by the following structure of Formula I:

Tenofovir is approved for commercial use as in the form of Tenofovir disoproxil fumaric acid salt, chemically known as 9-[(R)-2-[[bis[[(isopropoxycarbonyl)oxy]methoxy]phosphinyl]methoxy]propyl]adenine fumarate, is represented by the following structure of Formula:

Tenofovir disoproxil fumarate is a highly potent antiviral agent and is available in the market under the brand name VIREAD® in the form of 300 mg of oral tablets and in combination with other antiviral agents.
Patent publication WO 94/03467 (“the '467 publication”) discloses a process for preparation of tenofovir by reaction of 9-[2-(R)-hydroxy propyl)-N-benzoyladenine with di(2-propyl)-p-toluenesulfonyloxy methyl phosphonate in presence of a base such as sodium hydride in dimethyl formamide followed by dealkylation with bromotrimethyl silane in acetonitrile.
U.S. Pat. No. 5,733,788 (“the '788 patent”) discloses a process for preparation of tenofovir by reaction of 9-[2-(R)-hydroxy propyl)adenine with diethyl-p-toluenesulfonyloxy methyl phosphonate in presence of Lithium hydride in dimethyl formamide followed by dealkylation with bromotrimethyl silane.
U.S. Pat. No. 5,922,695 (“the '695 patent”) discloses a process for preparation of tenofovir by reaction of 9-[2-(R)-hydroxy propyl) adenine with diethyl-p-toluenesulfonyloxy methyl phosphonate and Lithium alkoxide base such as Lithium tert-butoxide in Tetrahydrofuran followed by dealkylation with bromotrimethylsilane.
U.S. Pat. No. 7,390,791 (“the '791 patent”) discloses a process for preparation of tenofovir by reaction of 9-[2-(R)-hydroxy propyl) adenine with diethyl-p-toluenesulfonyloxy methyl phosphonate in presence of Magnesium alkoxides such as Magnesium isopropoxide and Magnesium tert-butoxide in dimethyl formamide followed by dealkylation with bromotrimethyl silane.
Disadvantages associated with the '467 publication and the '788 patent are, usage of strong base alone such as sodium hydride and lithium hydride results in low conversion of the starting material, which leads to formation of unwanted by products and low product yields.
The '695 patent and the '791 patent discloses the use of highly expensive metal alkoxide bases such as Lithium tert-butoxide, Magnesium isopropoxide and Magnesium tert-butoxide; which in turn result to an increase in the manufacturing cost.
It would be desirable to provide a process for the preparation of tenofovir, which is simple and cost effective; and a process for its use thereof in the preparation of tenofovir disoproxil fumarate in a convenient, cost efficient manner and a commercial scale.
The present invention provides a process for the preparation of tenofovir, which involves use of a base and a metal salt for the conversion of 9-[2-(R)-hydroxy propyl)adenine into tenofovir. The process of the present invention can be practiced on an industrial scale, and also can be carried out without sacrifice of overall yield.